The present invention relates to a novel process for the preparation of .beta.-phenylethylchlorosilanes. More particularly, this invention is directed to the controlled addition reaction of a chlorosilane which contains at least one hydrogen atom bonded to silicon to styrene to produce a .beta.-phenylethylchlorosilane.
The addition of silanes containing at least one hydrogen atom bonded to silicon to unsaturated organic compounds in general, and styrene in particular, is known in the art. Generally, such addition results in a mixture of various isomers. For example, in the addition reaction of methyldichlorosilane to styrene using a platinum catalyst, some of the silicon-bonded hydrogen atoms of the silane molecules attach to the carbon atom nearest the benzene ring while the silyl radicals of the silane molecules attach to the carbon atom farthest from the benzene ring, and some of the silicon-bonded hydrogen atoms and silyl radicals attach in the opposite positions. Accordingly, there results from such addition reaction a mixture of .beta.-phenylethylmethyldichlorosilane and .alpha.-phenylethylmethyldichlorosilane. These reactions may be represented by the following equations respectively: ##STR1##
In the normal course of the addition reaction of a chlorosilane having at least one silicon-bonded hydrogen atom with styrene in the presence of a platinum catalyst, there is produced a mixture containing approximately 60 percent .beta.-phenylethylchlorosilane and approximately 40 percent .alpha.-phenylethylchlorosilane. The ratio of beta isomer to alpha isomer remains at approximately 60:40 regardless of whether a monochlorislane, dichlorosilane or trichlorosilane is utilized as the adduct.
Inasmuch as alpha isomers are usually unstable, the general tendency has been to avoid them. Wagner et al. reported, Ind. Eng. Chem. 45,367 (1953), the use of a platinum-on-charcoal catalyst to obtain an increased amount of beta isomer when reacting trichlorosilane and styrene at 200.degree. C. and under pressure for 20 hours. However, the use of platinum-on-charcoal catalyst to obtain a .beta.-phenylethylchlorosilane is accompanied by certain disadvantages. Thus, for example, where a platinum-on-charcoal catalyst is employed, the reaction tends to exhibit long inhibition periods before starting. Moreover, the mixing of large amounts of reactants to overcome such inhibition period is usually accompanied by extremely exothermic and violent reactions upon initiation. Additionally, the use of platinum-on-charcoal catalyst, as suggested by Wagner et al., results in the polymerization of substantial amounts of styrene with a corresponding decrease in yield of the desired addition product unless special precautions such as temperature control and/or large excesses of chlorosilane are employed.
Musolf and Speier reported, J. Org. Chem. 29,2519 (1964), that the addition of certain silicon hydrides to phenylalkenes of the formula: ##STR2## where n equals 0 to 4 and with chloroplatinic acid as the catalyst leads in each case to two products: ##STR3##
In their research Musolf and Speier studied examples with Y being equal to chlorine, fluorine or Me.sub.3 SiO and x equal to 0,1,2 and 3. The relative amounts of V to VI produced depended upon the nature of Y and the values of x and n. Substituents on the phenyl group in styrene also influenced the ratio of products of type V to products of type VI.
Pike and Borchert, U.S. Pat. No. 2,954,390, disclose that chlorosilanes having at least one silicon-bonded hydrogen atom can be added to styrene in the presence of tetrahydrofuran as solvent and platinum as a catalyst to provide the .beta.-phenylethylchlorosilane isomer exclusively. It is further disclosed that the reaction involving the addition of a chlorosilane having at least one silicon-bonded hydrogen atom to styrene can be controlled to produce substantially higher proportional yields of .beta.-phenylethylchlorosilanes over .alpha.-phenylethylchlorosilanes by conducting the reaction in the presence of a platinum catalyst and a highly polar organic ether solvent. Pike and Borchert suggest that the relative amount of beta isomer obtained is related to the polarity of the ether employed as solvent and to the ease with which the ether solvates the silicon atom of the silane employed in the reaction.
Koga et al., U.S. Pat. No. 4,242,272, disclose a method of producing an alkylphenylethyldichlorosilane comprising reacting a monoalkyldichlorosilane represented by the general formula RHSiCl.sub.2, wherein R is an alkyl radical of 3 to 20 carbon atoms, and styrene in the presence of a complex of platinum-phosphine compound at a temperature of 30.degree. C. to 200.degree. C., preferably 30.degree. C., to 110.degree. C. A reaction time of 1 to 60 hours is normally employed.
The principal object of the present invention is to provide an improved process for preparing .beta.-phenylethylchlorosilanes.
It is also an object of the present invention to provide a new and improved method of preparing .beta.-phenylethylchlorosilanes by addition of a chlorosilane having at least one silicon-bonded hydrogen atom to styrene in the presence of a platinum-type catalyst and a tertiary amine position-directing agent, whereby extremely exothermic and violent reactions are avoided and whereby large amounts of solvent are not required to effect formation of the beta isomer.